1. Field of the Invention
This invention relates to automatic gain control and more particularly to automatic gain control in hybrid analog and digital camera and imaging systems.
2. Description of Related Art
Conventionally, gain control in camera and imager devices and systems is subject to considerable technical limitations which make it difficult to use current cameras for professional and consumer applications. In particular, gain control is undertaken with an analog system or with a digital system, lacking integrated controls which are effective for both the analog as well as the digital portions of a combined camera system. There is a need to separately control gain over the analog and digital subsystems.
According to the present invention, a signal processing system (SPS) for an imager device includes a camera system for producing an imager signal; a correlated double sample (CDS) circuit for receiving data from an imager, which additionally operates as a variable gain amplifier (VGA) and is referred to herein as a CDS/VGA circuit; an analog-to-digital converter (ADC) coupled to the VGA circuit; a digital gain circuit (DGC) coupled to the ADC; and a histogram-based automatic gain control (AGC) circuit for controlling the CDS/VGA circuit and the digital gain circuit.
According to the present invention, gain control of a signal processing system for an imager device includes a correlated double sampler, a variable gain amplifier circuit for receiving data from the imaging system, and a histogram-based automatic gain control (AGC) circuit for controlling the level of gain provided to the camera system and a correlated double sampler and variable gain amplifier (CDS/VGA) circuit according to the present invention. The automatic gain control circuit allows for up to 98 dB of gain range including shutter exposure with an option for flickerless operation that is enabled with a hysteresis method according to the present invention.
Further according to the present invention, a processing system for an imager device includes a histogram-based automatic gain control (AGC) circuit coupled to the digital gain circuit for controlling the CDS/VGA circuit and the DGC. According to one embodiment of the invention, a distributed gain control circuit (DGCC) includes an automatic gain control (AGC) circuit for receiving an output digital level from the digital gain circuit for controlling the gain of the amplifier system and the digital gain circuit subject to a predetermined gain function (PGF). According to the present invention, a signal processing system (SPS) for an imager device includes an automatic gain control (AGC) circuit for controlling the VGA circuit and the DGC. According to the present invention, gain control of a signal processing system for an imager device includes an automatic gain control (AGC) circuit for controlling the level of gain provided to the camera system according to the present invention. Further according to the present invention, an automatic gain control circuit allows for up to 98 dB of gain range including shutter exposure with an option for flickerless operation that is enabled with a hysteresis method according to the present invention.